The newfound planet, named OGLE-2005-BLG-390Lb, has proven not for living

Subject: The newfound planet, named OGLE-2005-BLG-390Lb, has proven not for living Tue May 20, 2008 10:52 pm

An artist's conception shows the chilly planet OGLE-2005-BLG-390Lb with its home star in the distance. The star is about a fifth the mass of our sun, and the planet is about five and a half times as massive as Earth.

By Ker Thanupdated 1:19 p.m. ET Jan. 25, 2006

Astronomers on Wednesday announced the discovery of what is possibly the smallest planet known outside our solar system orbiting a normal star.

Its orbit is farther from its host star than Earth is from the sun. Most known extrasolar planets reside inside the equivalent of Mercury’s orbit.

The planet is estimated to be about 5.5 times as massive as Earth and thought to be rocky. It orbits a red dwarf star about 28,000 light-years away. Red dwarfs are about one-fifth as massive as the sun and up to 50 times fainter. But they are among the most common stars in the universe.

So the finding suggests rocky worlds may be common.

"The team has discovered the most Earthlike planet yet,” said Michael Turner, assistant director for the mathematical and physical sciences directorate at the National Science Foundation, which supported the work.

The discovery is detailed in Thursday's issue of the journal Nature.

More to comePrior to this discovery, the smallest extrasolar planet found around a normal star was about 7.5 Earth masses. Earth-sized planets have been detected, but only around dying neutron stars.

The newfound planet, named OGLE-2005-BLG-390Lb, is probably too cold to support life as we know it, astronomers said. With a surface temperature of 364 degrees below zero Fahrenheit (-220 degrees Celsius), it is nearly as frigid as Pluto.

It was discovered using a technique called “gravitational microlensing,” whereby light from a distant star is bent and magnified by the gravitational field of a foreground star. The presence of a planet around the foreground star causes light from the distant star to become momentarily brighter.

Astronomers hailed the discovery as the first of a new class of small, rocky worlds located at far-out distances from their stars.

The planet and star are separated by about 2.5 astronomical units. One AU is equal to the distance between the Earth and the sun. Until now, no small planet had been found farther than 0.15 AU from its parent star.

The finding means planet hunters are one step closer to detecting their holy grail: a habitable Earthlike planet that can sustain liquid water and support life.

"We may predict with reasonable probability that microlensing will discover planets with masses like that of Earth at a similar distance from their stars and with comparable surface temperature," said study co-author Bohdan Paczynski from Princeton University.